scholarly journals Measurement of particle accelerations in fully developed turbulence

2002 ◽  
Vol 469 ◽  
pp. 121-160 ◽  
Author(s):  
GREG A. VOTH ◽  
A. LA PORTA ◽  
ALICE M. CRAWFORD ◽  
JIM ALEXANDER ◽  
EBERHARD BODENSCHATZ
Keyword(s):  
Reynolds Number ◽  
Particle Physics ◽  
Large Scale ◽  
Low Reynolds Number ◽  
High Energy ◽  
Frame Rate ◽  
High Energy Particle ◽  
Particle Trajectories ◽  
Low Reynolds ◽  
Acceleration Component

We use silicon strip detectors (originally developed for the CLEO III high-energy particle physics experiment) to measure fluid particle trajectories in turbulence with temporal resolution of up to 70000 frames per second. This high frame rate allows the Kolmogorov time scale of a turbulent water flow to be fully resolved for 140 [ges ] Rλ [ges ] 970. Particle trajectories exhibiting accelerations up to 16000 m s −2 (40 times the r.m.s. value) are routinely observed. The probability density function of the acceleration is found to have Reynolds-number-dependent stretched exponential tails. The moments of the acceleration distribution are calculated. The scaling of the acceleration component variance with the energy dissipation is found to be consistent with the results for low-Reynolds-number direct numerical simulations, and with the K41-based Heisenberg–Yaglom prediction for Rλ [ges ] 500. The acceleration flatness is found to increase with Reynolds number, and to exceed 60 at Rλ = 970. The coupling of the acceleration to the large-scale anisotropy is found to be large at low Reynolds number and to decrease as the Reynolds number increases, but to persist at all Reynolds numbers measured. The dependence of the acceleration variance on the size and density of the tracer particles is measured. The autocorrelation function of an acceleration component is measured, and is found to scale with the Kolmogorov time τη.

Effect of Large Scale 3-D Structures on the Flow Around a Heated Cylinder at Low Reynolds Number

2018 ◽  
Vol 101 (2) ◽  
pp. 553-577 ◽  
Author(s):  
Stefano Rolfo ◽  
Konstantinos Kopsidas ◽  
Shahnurriman A. Rahman ◽  
Charles Moulinec ◽  
David R. Emerson
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Heated Cylinder ◽  
Low Reynolds

Numerical Design and Study of a MEMS-Based Micro Turbine

2005 ◽  
Author(s):  
Tatsuo Onishi ◽  
Ste´phane Burguburu ◽  
Olivier Dessornes ◽  
Yves Ribaud
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Skin Friction ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Low Reynolds ◽  
Micro Turbine

A full three dimensional Navier-Stokes solver elsA developed by ONERA is used to design and study the aerothermodynamics of a MEMS-based micro turbine. This work is performed in the framework of micro turbomachinery project at ONERA. A few millimeter scale micro turbine is operated in a low Reynolds number regime (Re = 5,000∼50,000), which implies a more important influence of skin friction and heat transfer than the conventional large-scale gas turbine. The 2D geometry constraints due to the limitation of fabrication technology also distinguish the aerothermodynamic characteristics of a micro turbine from that of conventional turbomachinery. Thus, for the foundation of aerothermodynamic design of micro turbomachinery, understanding of low Reynolds number effects on the performance is required and then the design of the turbine geometry can be optimized. In this study, aero-thermodynamic effects at low Reynolds number and different stator/rotor configurations are examined with a prescribed wall temperature. Losses due to heat transfer to walls and skin friction are estimated and their effects on the operating performance are discussed. Power delivery to turbine blades is checked and found satisfactory to give the objective design value of more than 100W. The effects of turbine exhaust geometry and the number of blades on turbine performance are also discussed.

Fluid Mechanics of Longitudinal Contractions in the Small Intestine

1979 ◽  
Vol 101 (4) ◽  
pp. 284-288 ◽  
Author(s):  
J. G. Melville ◽  
N. Denli
Keyword(s):  
Reynolds Number ◽  
Small Intestine ◽  
Motor Activity ◽  
Fluid Mechanics ◽  
Low Reynolds Number ◽  
Retrograde Flow ◽  
Particle Trajectories ◽  
Low Reynolds

Longitudinal contractions in the duodenum are shown to exit experimentally. A low Reynolds number model of flows induced by propagating longitudinal contractions is presented for circular conduits. Particle trajectories and time lines are shown to elucidate the flowfields. Longitudinal motor activity is shown to have the capability of satisfying the mixing function of the small intestine and to be a possible contributor of retrograde flow.

Very-large-scale fluctuations in turbulent channel flow at low Reynolds number

2016 ◽  
Vol 62 ◽  
pp. 593-597
Author(s):  
Masaharu Matsubara ◽  
Shun Horii ◽  
Yoshiyuki Sagawa ◽  
Yuta Takahashi ◽  
Daisuke Saito
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Large Scale ◽  
Low Reynolds Number ◽  
Turbulent Channel Flow ◽  
Low Reynolds

Separation-Bubble-Transition Measurements on a Low-Re Airfoil Using Particle Image Velocimetry

2005 ◽  
Author(s):  
B. R. McAuliffe ◽  
M. I. Yaras
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Large Scale ◽  
Particle Image ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Low Reynolds

This paper presents experimental results on separation-bubble transition at low Reynolds number and low freestream turbulence, measured on an airfoil using particle image velocimetry (PIV). The two-dimensional PIV measurements have been performed over the suction surface of a low-Reynolds-number airfoil in a water tow-tank facility. Reynolds numbers, based on airfoil chord length and towing speed, of 40,000 and 65,000 have been examined at various angles of incidence, providing a range of streamwise pressure distributions and transitional separation-bubble geometries. The types of bubbles observed range from a short and thick bubble with separation near the leading edge of the airfoil, to a long and thin bubble with separation far downstream of the suction peak. The PIV measurements facilitate visualization of the vortex dynamics associated with separation-bubble transition. The growth of instability waves within the separated shear layer and eventual breakdown into turbulence is documented through the instantaneous vector fields. For all cases examined, large-scale vortex shedding and multiple reverse-flow zones are observed in the reattachment region. A technique for estimating the location of transition onset based on statistical turbulence quantities is presented, and comparisons are made to existing transition models.

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